The bitter taste of danger
Survival of mammals in their environment depends on their ability to interpret information about their neighborhoods. For example, rodent preys have evolved under predation pressure and avoid to be eaten by using, in a complementary manner, their senses. In particular, mice have developed an elaborate sense of smell to decipher a variety of chemicals signaling threatening situations. Indeed, molecules released by stressed or injured conspecifics (alarm pheromones), as well as volatiles involuntary emitted by predators (kairomones) are typical cues detected, in mice, by the neurons of the Grueneberg ganglion, an olfactory subsystem devoted to the detection of these chemical cues indicating an impending danger. These GG neurons use a bitter taste signaling pathway to detect these danger cues. Indeed, using the molecular structure of the previously identified GG ligands as bait, we screened chemical libraries and found a new category of cues previously identified as bitter tastants that evoked neuronal responses in mouse GG neurons and initiated fear-related behaviors in a GG and in a volatility-dependent manner. Moreover, we found in the GG the expression of specific bitter signaling elements implicated in their tongue recognition such as bitter taste receptors (TAS2Rs) and their associated G protein (GNAT3). In particular, we identified in a heterologous expression system that the TAS2R143 is a chemical danger cues receptor transducing both alarm pheromone and predator-derived kairomone signals.